Fire alarm



May 17, 1949.

I. O. MOBERG FIRE ALARM Filed Jan. 3, 1946 2 Sheets-Sheet 1 Patented May17, 1949 UNITED STATES FATENT OFFICE 2,470,711 F R ALARM Ivar O.Moberg,'Lowell, Mass. Application January 3, 1946,. Serial No. 638,835

This invention relates to automatic fire alarms and fire alarm systemsof a type suitable for use in dwellings and other buildings in whichelaborate forms of apparatus of this character are too expensive to beafforded. It is an important ob-* ject of this invention, therefore, todevise an exceptionally simple apparatus of this character which can bemanufactured and installed economically, but which will be thoroughlypractical and reliable.

The nature of the invention will be readily understood from thefollowing description when read in connection with the accompanyingdrawings, and the novel features will be particularly pointed out in theappended claims.

In the drawings,

Fig. 1 is a front elevation of a preferred form of fire alarm embodyingthis invention;

Fig. 2 is a side elevation of the apparatus shown in Fig. 1;

Fig. 3 is a diagrammatic view of a system embodying features of thisinvention;

Fig. 4 is a side view of a switch unit designed for use in the systemshown in Fig. 3; and

Fig. 5 is a front view of the device shown in Fig. 4 with some partsbroken away. 7

Referring first to Figs. 1 and 2, the construction there shown comprisesan electric gong ZClaims. (017177-311) the name of Vinyon fiber ispreferred.

migh t make it unreliable.

non-absorbent, non-inflammable, except upon 1 of a 'copolymer of vinylchloride and vinyl acetate. That available commercially under It has theadvantage of being exceptionally stable and unaffected by the commonagents which For example, it is direct exposure to flame, permanentlywaterresistant,'mi1dew-proof, and is acid-proof for all practicalpurposes important in connection with this invention. While theunstretched Vinyon yarn has a very low tensile strength, the stretchedvarieties are very strong. One form known as ST Vinyon yarn ispre-stretched about 50%, while another, known as HST, is pre-stretched100%. These both have surprisingly high tensile strength. Also, bothhave the characteristics,

valuable for the purposes of this invention, of rewith the usualvibrating hammer 4, and the customary, or any other suitable means, foractuating said hammer, said means being enclosed in the casing 5. In thearrangement shown, the panel 2 forms the front of a box or casing 6 inwhich a dry battery I, or some other convenient source of electriccurrent, such as a bell transformer, is mounted.

For the purposes of this invention, the operating circuit for the bellis controlled by a simple form of switch comprising a wire arm 8, aportion of which is wound around the screw 9 to form a spring l0, Fig.2, the screw anchoring the spring to the panel. Cooperating with thisarm are two stationary contacts a and 12, both formed on, or secured to,a contact plate l2 which is screwed to the panel 2, and the arm carriesa contact c positioned between the stationary contacts a and b andadapted to engage either of them. The free end of the spring switch arm8 terminates in a hook 8" to which a length l3 of thermoplastic thread,string, cord, or other filamentary material, hereinafter referred togenerically as thread, is secured, its opposite end being fastened to abinding post l4.

According to this invention the thread I3 is 'maining very stable as tolength, as their temperature is raised, up to about 148 F. At this pointthe thread contracts about 5% in length and contraction continues as thetemperature rises until either the melting point of 260 F. is reached orthe thread has contracted to its original length. Once contracted, thethread remains stable in length at decreasing temperatures. Thischaracteristic is used in the apparatus shown in Figs. 1 and 2. Assumingthat the assembly there shown is in operation, and the temperature ofthe thread I3 is raised to some point above 148 F., the thread willcontract, thus bringing the contact 0 into engagement with the contactI). This completes a circuit from the battery terminal l5 through theconductor l 6, spring switch arm 8, contacts 0 and b, and wire l1,through the bell solenoid and conductor I8, to the other batteryterminal 20.

If the fire should reach the thread l3, or it should become broken forany reason, then the switch arm 8 is released, thus bringing the contact0 into engagement with the contact a and closing the bell circuit again.

Thus the alarm is sounded either upon its rupture or overheating, thatis the raising of the temperature of the thermoplastic thread l3 abovethe critical point in the neighborhood of 148 F.

Because of the nature of fibers made of the copolymer above designated,there is practically no danger of the thread [3 deterioratingsufliciently to render the device inoperative, and a very infrequentinspection of the apparatus is sufficient to determine the operativenessof the electrical elements of the apparatus.

The apparatus may be located in any con- 3 venient spot where it isbelieved that fire is most likely to occur as, for example, by hangingit on a hook, an aperture 2|, Fig. 1, being provided in the casing 6 forthis purpose. When it is desired to use any substantial number of thesealarms located at difierent points in the building, a series ofindependent units, such as that shown in Figs. 1 and 2, may be employed,or a single unit of this nature may be connected up to a number ofswitch units so that ithezrupture tor cnntmctionof the controllingelement I3 at anyone-mt these points will sound the alarm.

A switch unit suitable for this purpose is shown in Figs. 4 and 5 inwhich the parts corresponding to those shown in Figs. 1 and 2 aredesignated by the same, but primed, numerals. .lilene the spring arm 8'is arranged as before withits contact 0 operating between'upperand'*lower=cooperating contacts a and b, and the;;plateilflf.

on which the latter aremounted, is provided with 20 ,a terminalbindingscrew 22. The thread L3 ,is

tensioned between the hook of the 'springarm and the binding post [4..Eor convenience :in installation it is usually preferable totconnect,the

spring 10' by a conductor 123$.to a-iterminal screw "rise above itscritical temperature, or shouldfbu-m .ofisor' become broken, the .alarmwill immediately be sounded and .warning givenn'f the .pvefiheatin,orffailure of one of the thermoplastic "Thus the invention provides ;a.very simple, reliable and inexpensive form. of fire .alarm which can bequickly installedby .any .one {familiar with simple electrical circuits,or even by ".the Ihouseholder himself.

While I have herein shown and described a preferred embodiment of,myinvention it istcontemplated that the invention .may .be embodied inother ,iorms withoutdeparting from the spirit orscope thereof.

Having thus described my invention, what I .desire to claim 7 as anewis:

1. An apparatus of the character described, comprising an electricallyoperated alarm device, an electric circuit in which said device isoperatively connected, 9, switch in said circuit comprisin a movablecontact and two stationary contacts, said movable contact being locatedbetween said stationary contacts, a means connected with said movablecontact and tending to move the latter into engagement with one of said10 @atationary contacts, and aithread connected with $83! movablecontact and holding it normally in its open position, said thread beingcomposed (essentially of a, .copolymer of vinyl chloride and ivinylacetate and being prestretched, whereby it operates upon overheating toshrink and thereby itmcloseathe circuit through one of said stationarycontacts and .upon rupture to close the circuit through "the other ofsaid stationary contacts.

RNA-n apparatus of the character described, comprising an arm carrying aswitch contact, stwoiadditionalccontactsbetween which thecontactxrmvable .withsaidarm operates, and aprelstretchedathread,composedessentially of a copoldimer of .vinyl,chloride and vinyl acetate coninettteditmsaid arm .and controlling theengagemerit :01 ithe latter-contact with one of saidadditionalpontacta-wherebythe,rupture of the thread,permitssaidiarmtdmove.its contact into engage- ..ment ,Wit h tone .ofsaid :additional contacts and the shrinkage of said thread byoverheating ,causesitltozmove,saidarm sufiiciently to make its :cuntactenga e ,the other of said additional rnrrtactssand wielding, 1111531115connected with said rmvabtetcontact iorlurging thesame toward'one -0:said additional :contacts.

IVAR O. -MOBERG.

.CITED iliize ffiollnmingreferences are of record in the l l file ofthis patent:

UNIQREE :SZIATES PATENTS Number Name .Date

film-M5 Cantrell Dec. 5 1893 8&73310' Bestul Mar. 19, 1907 1,132,103-McGlanaha-n Mar. 16,1915

'EQREIGN PATENTS :1hunizer ,Country Date rGreatBritain Aug. 13, 1943

